1899.] A. Alcock — Garcinological Fauna of India. 49 



median frontal teeth are larger and broader than the 

 two outermost pairs. A spine at the end of the poste- 

 rior border of the arm may be present, or not Gonioneptunus, 



Key to the Indian species of the genus Charybdis ( = Goniosoma.) 



I. The antennal flagellum is completely excluded from 

 the orbital hiatus : the ridge that bounds the dorsum 

 of the carapace posteriorly forms a curve with the 

 postero-lateral borders : no spine on posterior border 

 of arm (Goniosoma) : — 



A. No distinct transverse ridges on the carapace 

 iehind the level of the last spine of the antero- 

 lateral borders : — 



1. Not more than three large spines on the 

 anterior border of the arm : the orbits 

 have no decided dorsal inclination and 

 their major diameter is never more than 

 one- third the width of the interorbital 

 space : — 



a. First spine of antero-lateral border 

 anteriorly truncated and notched : 

 sixth abdominal tergum of male 

 with curved and gradually conver- 

 gent sides Q. cruciferum, 



b. First spine of antero-lateral border 

 obliquely truncated with the inner 

 angle acute : sixth abdominal ter- 

 gum of male with curved and 

 gradually-convergent sides : epi- 

 branchial regions extremely tumid 



dorsally 0. RiverS'Andersoni. 



c. First spine of antero-lateral border 

 acute : the sides of the sixth abdo- 

 minal tergum of male parallel or 

 slightly divergent in two-thirds or 

 more of their extent : — 



i. An acute spine on the posterior 

 border of carpus of last pair 



of legs G. merguiense. 



ii. A sharply dentiform lobule at 

 the outer end of the lower 



border of the orbit G. quadrimaculatum, 



• iii. The major diameter of the 

 true orbital cavity is barely a 

 fourth the width of the inter- 

 orbital space G. annulatum, 



2. Four or more large spines on the anterior 

 border of the arm : the orbits have a 

 strong dorsal inclinatiou and their major 



J. II. 7 



